1. Field of the Invention
The present invention relates to a liner with which the interior of a manhole is lined (hereinafter called "manhole liner") and a method for lining a manhole; and in particular it relates to a manhole liner impregnated with a thermosetting resin and a method for lining a manhole with such a liner.
2. Description of the Prior Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038 (counterpart U.S. Pat. No. 4,581,247).
According to this publication, this method of pipe mending comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, such as air and water. The tubular liner bag is made of a flexible resin-absorbent cloth material impregnated with a thermosetting (heat-curable) liquid resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is very long and closed at one end and open at the other. The tubular flexible liner bag is first flattened, then, the open end of it is made to gape wide and hooked (anchored) at one end of the defective or old pipe in a manner such that the wide-opened end of the liner bag completely and fixedly covers and closes the pipe end; a portion of the liner bag is pushed into the pipe whereby an annular pocket is made; then, a pressurized fluid is applied to the pocket portion of the tubular liner bag such that the fluid urges the tubular liner bag to enter the pipe. Since one end of the tubular liner bag is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag proceeds deeper in the pipe as it is turned inside out. (Hereinafter, this manner of insertion shall be called "everting" or "oeversion".) When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner bag is pressed against the inner wall of the pipe by the pressurized fluid or by an inflatable pressure bag (intra-liner bag) later introduced into the pipe, and the tubular flexible liner bag is hardened as the thermosetting liquid resin impregnated through the thickness of the liner bag is heated, which is effected by heating the pressurized fluid filling the tubular liner bag by means of a hot steam, etc. Thereafter, the pressure bag is removed the closed end of the liner bag is cut off. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
Now, it is also possible to adopt part of this method in a course of lining a manhole.
For instance, as shown in FIG. 33, a sewer pipe 120 is first plugged with a plug 122 at a location upstream to a manhole 121 to be repaired so as to stop the drain water from flowing into the location of lining; then, a tubular manhole liner bag 101 is inserted into the manhole 121 from the ground surface. Here, depending upon the size of the manhole, the insertion of the manhole liner bag 101 can be done by eversion. Thereafter, while the liner bag 101 is pressed against the inner wall of the manhole 121, the thermosetting liquid resin, with which the tissue of the liner bag 101 is soaked, is cured to harden, whereby the inner wall of the manhole 121 is lined with a rigid liner 101. Incidentally, until this lining operation is over, the drain water running in the sewer pipe 120 is drawn out by means of a pump 140 at a location upstream to the plug 122, and the drawn water is transported to some other place, and in most cases back into the pipe 120 at a downstream location.
By the way, as shown in FIG. 33, generally the upper part of a manhole is formed with a reducer portion, where the hole is converged upward such that the manhole is narrowest at its uppermost end.
Now, before lining the manhole 121 with the liner 101, a plurality of ladder steps, not shown, which are rigidly fastened to the inner wall of the manhole 121 in a descendent row, are removed, and when the manhole 121 is newly lined with the liner 101, holes are made at intervals through the rigid liner 101 and partially into the wall of the manhole 121, and, then, a plurality of new ladder steps 147 are hit in these holes and fastened therein, as shown in FIG. 34.
Also, when the liner bag 101 is hardened inside the manhole 121 it becomes very hot and as it cools down its size is reduced so that there is created a gap between the inner wall of the manhole 121 and the liner bag 101. In order to fill up this gap, holes are made through the liner bag 101, and a curable liquid filler is injected through these holes into the gap between the manhole inner wall 121 and the liner bag 101.